The current invention addresses the need for a portable, disposable means of monitoring flow rate in infusion therapy especially in cases where medication administered is toxic or has a narrow therapeutic range. The measurement or monitoring of flow rate will have to be non-contact.
The measurements of heat pulse, especially via non contact means are always fraught with complexities. The impact of thermal dynamics and kinematics resulting from the interplay of thermal coefficient, thermal mass, heat loss due to emissivity and conduction of heat along the channel carrying conduit when velocity changes makes flow rate determination by measurement of flow rate by mathematical relationship derived from single or even multiple parameters limited in its applications.
The measurement of flow rate by measuring the time for heat pulse to flow between two points is known (U.S. Pat. No. 4,813,280). The flow rate is inversely proportional to the time. A flow rate range of 48 ml-144 ml/Hour (Hr) is possible by means of the flow cell construction disclosed. The fluid channel has an over sleeve which acts as barriers preventing contact between thermal probes and the fluid. Thermal probes used as heat source and sensor require very thin barriers so that the measurement accuracy is not compromised. The flow cell construction results in creating an inner diameter about 0.1 inch (2.54 mm) or a cross sectional area 4.0 mm2(smaller dimensions presumably do not allow engagement of the probes).
In U.S. Pat. No. 4,938,079, a non contact flow measurement based on the change in resonance of a microwave signal with the passage of the thermal marker is disclosed. The thermal marker could be produced by conventional heating of one with microwave radiation. The setup is complex and is intended for closed loop flow-measurement where measured output is used to adjust flow rate. The technology used renders it impractical as a mobile device.
Limitations in applications of prior art makes the creation of a device with the above mentioned requirements non existent, despite the patents were issued 20 or more years ago.